High-efficiency fiber-cladding power stripper based on all-dielectric optical thin films.

Although conventional fiber-cladding power strippers (CPSs) based on the techniques of high-index adhesive or corrosive liquids onto fiber inner cladding have been well developed, they are still facing challenges in special applications such as spaceborne or radiation-environment fiber lasers and amplifiers. In this paper, we propose and fabricate high-efficiency CPSs based on all-dielectric optical thin films. By numerically analyzing the propagation characteristics of cladding light at the thin film interface, we design a high-index T a 2 O 5 CPS and A l 2 O 3 CPS with single- and cascaded-layer films coated onto the fiber inner cladding, respectively. In our experiment, the CPSs are successfully fabricated onto the inner-cladding surface of 10/125 double-clad fiber based on ion-beam-assisted deposition technology. The stripping efficiency for the 976 nm residual cladding power was measured up to 99.38%, and the stripping power of the fiber CPS without active cooling can be 24 W at least. Such CPS could be advantageous for applications in spaceborne-based fiber lasers or amplifiers (e.g., gravitational wave detection, spaceborne lidar).

All-fiber cyan laser at 491.5 nm.

We report, for the first time to our knowledge, a compact continuous-wave all-fiber cyan laser. The all-fiber cavity consists of a 443-nm fiber-pigtail laser diode as pump source, a 4.5-cm single-clad Pr3+-doped fluoride fiber, and two custom-built dielectric-coated fiber-pigtail mirrors in the visible spectral region. Downconversion cyan lasing at 491.5 nm is directly achieved, providing a maximum output power of 97.5 mW with a slope efficiency of 23.7% and a power fluctuation of less than 0.41%. Such a compact all-fiber cyan laser may be of great significance to expand the color reproduction range of laser displays, and has potential applications in fluorescence imaging, underwater communication, and detection.

1.3/1.4 µm dual-wave band dissipative soliton resonance in a passively mode-locked Bi-doped phosphosilicate fiber laser.

We report the 1.3/1.4 µm dual-wave band dissipative soliton resonance (DSR) in a passively mode-locked bismuth-doped phosphosilicate fiber (Bi-PSF) laser. The low-water-peak Bi-PSF with two bismuth active centers associated with silicon and phosphorus supports the O+E-band gain. Using a 1239 nm home-made Raman fiber laser as pump source and nonlinear amplifying loop mirror for initiating mode-locking, stable DSR operation at 1343 and 1406 nm is achieved with the spectral bandwidth of 12 and 16 nm. The pulse duration with the pump power increases from 62 to 270 ps with a repetition frequency of 4.069 MHz. The average power is 11.05 mW corresponding to the maximum energy of 2.7 nJ. This is, to the best of our knowledge, the first demonstration of a mode-locked fiber laser in the ∼1.38 µm water absorption band and the O+E dual-wave band operation for applications in all-spectral-band communications, bio-medical imaging, and terahertz difference frequency generation.

Intermode beating mode-locking technique for a rare-earth-doped fiber pulsed laser.

In this paper, we report the intermode beating mode-locking of a 2 µm Tm3+-doped fiber laser (TDFL) pumped by a 1565 nm continuous-wave multi-longitudinal-mode laser. Because strong intermode beating of the 1565 nm pump source induces the periodic modulation of 2 µm intracavity power, stable mode-locking of the TDFL is successfully established by precisely matching the 2 µm cavity frequency with the intermode-beating frequency of the 1565 nm pump source. The mode-locked laser, without requiring any specific mode-locking element, can stably emit the rectangular nanosecond pulses. The mode-locking operation at the center wavelength of 1980.35 nm has a >61 dB signal-to-noise ratio and a 34.496 MHz repetition rate. Although the preliminary results are not better than those of conventional mode-locking, intermode beating mode-locking in combination with rare-earth-doped fiber lasers could provide a promising and alternative solution for compact, low-cost, and high-performance pulsed laser sources.

1.2-W average-power, 700-W peak-power, 100-ps dissipative soliton resonance in a compact Er:Yb co-doped double-clad fiber laser.

Mode-locked pulses in the dissipative soliton resonance (DSR) regime enable extremely high pulse energy, but typically have the limited peak power of <100 W and a nanosecond-long pulse duration. In this Letter, we demonstrate high-peak-power, ultrashort DSR pulses in a compact Er:Yb co-doped double-clad fiber laser. The linear cavity is simply formed by two fiber loop mirrors (FLMs) using a 50/50 optical coupler (OC) and a 5/95 OC. The 5/95 FLM with a short loop length of 3 m is not only used as the output mirror, but also acts as a nonlinear optical loop mirror for initiating high-peak-power DSR. In particular, the mode-locked laser can deliver ∼100 ps DSR pulses with a maximum average power of 1.2 W and a peak power as high as ∼700 W. This is, to the best of our knowledge, the highest peak power of DSR pulses obtained in mode-locked fiber lasers.

Bidirectional operation of 100 fs bound solitons in an ultra-compact mode-locked fiber laser.

We report on the experimental observation of bidirectional 100-fs bound solitons from a nanotube-mode-locked dispersion-managed Er-fiber laser with an ultra-simple linear cavity. Two mode-locked pulse trains in opposite directions are delivered simultaneously from the linear cavity. Under the pump power of <74 mW, both the bidirectional outputs of the laser work at the single-soliton state with pulse duration of 173 fs and 182 fs, respectively. Once the pump power is more than 74 mW, both the bidirectional outputs evolve into the two-soliton bound states with soliton separation of 1.53 ps. Interestingly, the bidirectional operations can show the different bound states, i.e. the forward bound solitons with phase difference of + π/2, and the backward ones with phase difference of -π/2. This is, to the best of our knowledge, the first demonstration of such compact bidirectional soliton fiber laser with the sub-200 fs pulses.

Compact self-Q-switched green upconversion Er:ZBLAN all-fiber laser operating at 543.4 nm.

We report the demonstration of a compact self-Q-switched green upconversion Er3+:ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber laser operating at 543.4 nm. The all-fiber green laser simply consists of a 45 cm high-concentration Er3+:ZBLAN fiber, a 976 nm pump source, and a pair of fiber end-facet mirrors. Under the strong excitation of the 976 nm pump laser, green upconversion lasing at 543.4 nm is achieved from the compact Er3+:ZBLAN fiber laser. Interestingly, the green laser exhibits stable self-Q-switching operation. As the 976 nm pump power is increased, the pulse repetition rate linearly increases from 25.9 to 50.8 kHz and the pulse width narrows from 7.2 to 1.95 µs. The Q-switched green laser has a pump threshold of 118 mW and a maximum output power of 6.9 mW with a slope efficiency of 30%. This is, to the best of our knowledge, the shortest-wavelength operation of a self-started or passively Q-switched fiber laser.